/Engine/Source/Runtime/Slate/Public/Framework/MultiBox/MultiBoxBuilder.h
Adds a button to a row
void AddButton ( const [FText](API\Runtime\Core\Internationalization\FText) & InLabel, const [FText](API\Runtime\Core\Internationalization\FText) & InToolTip, const [FUIAction](API\Runtime\Slate\Framework\Commands\FUIAction) & UIAction, const [FSlateIcon](API\Runtime\SlateCore\Textures\FSlateIcon) & InIcon, const EUserInterfaceActionType UserInterfaceActionType )